Oxide coated metal pigments and film-forming compositions

ABSTRACT

This invention relates to sacrificial-metal pigments coated with an effective amount of at least one metal oxide or a combination of metal oxides such as a mixture of chromium and zirconium oxides, and the process for preparing said coated pigments and combination thereof with film-forming binders for coating metal substrates to inhibit corrosion. The coated sacrificial-metal pigments are electrically active to prevent corrosion of metal substrates that are more cathodic (electropositive) than the metal oxide coated metal pigments.

This application is a Division of copending application Ser. No.13/564,341 filed Aug. 1, 2012 which-in-turn is a continuation-in-part ofco-pending application Ser. No. 13/192,158 filed Jul. 27, 2011which-in-turn is a continuation-in-part of application Ser. No.13/010,830, filed on Jan. 21, 2011.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefore.

FIELD OF THE INVENTION

This invention relates to sacrificial-metal pigments coated witheffective amounts of corrosion inhibitors and combinations of saidcoated metal pigments with film-forming binders for application to metalsubstrates. The combination of the coated pigments and the film-formingpolymeric binder results in an electrochemically active coatingcomposition which provides cathodic protection to various metalsubstrates.

Metal surfaces require the protection of coatings especially when thesurfaces are exposed to corrosive environments. Metal surfaces ofaircrafts, for example, are exposed to seawater which requiresprotection from corrosion. Specifically, aircrafts, e.g., Navyaircrafts, are exposed to seawater spray in addition to variousacid-forming gases such as sulfur dioxide and the like. In addition toaircrafts, machinery and equipment in the industrial environments, wherefossil fuels are used, also needs protection against corrosion. It isimportant therefore that the coating on the pigment be resistant tocorrosion, including chemicals, the weather and at the same time beflexible and have good adhesion to the various metal substrates.

BACKGROUND

Metallic pigments are known to provide electrochemical, electrical,thermal, and other properties to compositions which are used forprotecting various materials such as metal from corrosion, maintainingelectrical conductivity, shielding equipment from electromagneticfields, resisting elevated temperatures, and providing protection frommoisture. Silver, gold and other noble metal pigments are used for theirelectrical conductivity and thermal conductivity properties. Zinc andmagnesium are used for their electrochemical properties. Aluminum isused for its thermal and chemical barrier properties. A majorshortcoming of the noble metals is their strong cathodic potential. Whenused in products for electrical and thermal management, the noble metalscoupled with anodic materials such as aluminum alloys are used forelectrical equipment.

For example, metals such as zinc and magnesium are used in curedcoatings to provide corrosion resistance to the metal on which they arecoated. Typical zinc-rich primers use zinc “dust” which is approximately5 micron zinc powder. This zinc powder is added untreated to variousresins, organic and inorganic. Zinc-rich coatings are used mostly onsteel to slow down the onset of rust or corrosion. A common secondaryproblem with zinc-rich coatings is the rusting or corrosion of the zincpowder in the coating while it is protecting the steel. When zinccorrodes, it typically forms a white residue which can discolor theobject being protected and is not desired for aesthetic reasons. Thiszinc self-corrosion also “uses up” the zinc and reduces the effectivelife of the zinc-rich coating.

Other metals, such as magnesium has been used in combination with zincand by itself in similar coatings to protect steel and aluminumrespectively. Magnesium also is prone to forming white corrosionproducts which discolor the object being protected and is undesirablefor aesthetic reasons. A second application of coatings with metalpigments is for electrical and thermal conductivity. Silver, nickel,copper and aluminum are good conductors of electricity and heat. Silverand nickel are commonly used as pigments in conductive coatings on othermaterials like glass, carbon/graphite, and aluminum which are lighterand less expensive. Copper is an excellent bulk conductor but is nottypically used as a conductive pigment as it oxidizes quickly and losesits ability to conduct electricity effectively in coatings. Aluminum isan excellent bulk conductor, but it also oxidizes easily in the naturalenvironment and is not effective as a conductive pigment in coatings. Athird application is the protection of iron and iron alloy (steel)particles from rusting due to exposure to the environment. Theseparticles are used in coatings for their magnetic properties and tend tored rust and lose effectiveness over time due to exposure to theenvironment.

Specifically, this invention relates to a composition and to a processfor preparing and applying a semi-conducting coating comprising at leastone metal oxide onto metal particles and the use of these coatedparticles in coatings designed to protect substrates from corroding andprovide electrical or thermal conductivity.

More specifically, this invention relates to compositions of thesecoated particles in various compositions, such as greases and othervehicles which are used to protect substrates from corroding (zinc ormagnesium) and to provide an electrically and thermally conductive pathon surfaces which have insufficient conductivity (silver, nickel,aluminum, copper) or for magnetic properties (iron). The conductivecoatings are typically used for electromagnetic shielding, staticdissipation, continuity, and thermally conductive pathways in the caseof flexible circuits and similar applications. These metals aretypically used at high purity for maximum conductivity or coatingefficiency. This invention covers all of these potential alloys as longas the key property of cathodic protection (magnesium and zinc) orelectrical conductivity (silver, nickel, copper and aluminum) aremaintained. For example, zinc can be alloyed with nickel to yield aparticle with tailored open-circuit potential and controlled activity.This alloy can be coated effectively with the semi-conducting coatingdescribed by this invention to control the corrosion or white rusting ofthe zinc in the alloy.

It is therefore an object of this invention to incorporateelectrochemically active coated-pigments into a binder to providecathodic protection to metal substrates.

It is another object to provide cathodic protection to metal substratesby coating the substrate with a sacrificial-anode coating that keeps theelectrochemical potential of the substrates negative to prevent itscorrosion.

It is a further object of this invention to provide metal pigmentscontaining effective amounts of a corrosion-resistant oxide coating andthe use of these oxide coated pigments in film-forming binders as acoating for metal substrates.

DESCRIPTION OF DRAWINGS

FIG. 1 shows the performance of two coatings on 7075-T6, an aluminumsubstrate, after exposure to the ASTM B117 salt fog for 500 hours. Thecoated particles are more resistant to self-corrosion which leads towhite zinc oxide that is visible on the coating with the untreated zinc.Compare the coatings on 7075-T6 aluminum with untreated zinc particlesin epoxy (left) and with treated zinc particles (right) after 500 hoursexposure to ASTM B117, as shown in Example 10.

A composition identical to Example 10, except that the particles were 20micron aluminum particles treated per Example 1 and the untreatedsubstrate. FIG. 2 shows the performance of the two coatings on 7075-T6aluminum after exposure to the ASTM B117 salt fog for 500 hours. It isclear that the coated particles of this invention are more resistant toself-corrosion which leads to white aluminum oxide that is visible onthe coating containing the untreated aluminum particles. Compare thecoatings on 7075-T6 aluminum with untreated aluminum particles in anepoxy resin (left) and with the treated aluminum particles (right) after500 hours exposure to ASTM B117.

Composition of corrosion-resistant epoxy primer made with coated zincand magnesium particles. An identical composition to Example 10, exceptthat the particles were a mixture of 75% 5 micron zinc particles and 25%100 micron magnesium particles treated and untreated. FIG. 3 shows theperformance of the two coatings on 2024-T3 aluminum after exposure tothe ASTM B117 salt fog for 500 hours. The coated particles are moreresistant to self-corrosion which leads to white zinc and magnesiumoxide that is visible on the coating with untreated particles. Coatingson 2024-T3 aluminum with untreated zinc and untreated magnesiumparticles in an epoxy resin (left) and with coated zinc and magnesiumparticles (right) after 500 hours exposure to ASTM B117.

FIG. 4 shows the performance of conductive grease made with coatednickel particles. Greases made per Example 9 with uncoated and coatednickel particles were applied to 2024-T3 aluminum panels and assessedfor electrical performance and corrosivity of the grease to the aluminumsubstrate. The uncoated nickel grease gave a dc resistance of 0.8milliohms when applied between two aluminum panels torqued to 20inch-pounds. The coated grease gave a dc resistance of 1.89 milliohms insimilar test. This compares to 3.3 milliohms for a 15 volume percentsilver grease reference. For an application of interest, a 2.5 milliohmresistance or lower must be obtained. This data shows that the coatednickel still meets the electrical requirement. The photos show thecorrosivity of the uncoated and coated nickel greases on 2024-T3aluminum that was exposed to ASTM B117 salt fog for 24 hours. FIG. 4shows the aluminum after the grease was removed after the exposure. Theuncoated nickel grease caused significant pitting and corrosion of thealuminum under the grease.

The coated nickel grease only caused minor surface oxidation, with nopitting. This shows significant reduction in corrosivity of the greasewhile maintaining required electrical conductivity. The silver referencegrease is shown as well. It caused even more damage to the aluminumsurface than the uncoated nickel, as expected since silver is morecathodic than the nickel. FIG. 4 specifically shows Aluminum 2024-T3panels after exposure to 24 hours of ASTM B117 salt fog in contact withuncoated nickel grease (left), coated nickel grease (center) anduncoated silver reference grease (right).

FIG. 5 shows the performance of conductive grease made with coatedaluminum particles. Greases made per Example 9, except with uncoated orcoated aluminum particles per Example 1 were applied to a 2024-T3aluminum panels and assessed for electrical performance and corrosivityof the grease to the aluminum substrate. FIG. 5 shows the corrosivity ofthe uncoated and coated aluminum greases on 2024-T3 aluminum that wasexposed to ASTM B117 salt fog for 24 hours. The figure shows thealuminum after the grease was removed after the exposure. Neither greasecaused corrosion of the aluminum substrate. This is not unexpected sincethe open circuit potentials of the aluminum particles and aluminumsubstrate are similar, but validates that the coating on the aluminumparticles does not change their corrosivity on the aluminum substrate.FIG. 5 specifically shows Aluminum 2024-T3 panels after exposure to 24hours of ASTM B117 salt fog in contact with uncoated aluminum grease(left) and coated aluminum grease (right).

FIGS. 6(a) and 6(b) show the process of example one where FIG. 6(a) isthe transmission electron micrograph and FIG. 6(b) shows the mono-EDSline profiles.

SUMMARY OF THE INVENTION

This invention is directed to coated metal pigments which have aparticle size ranging from about 2 to 100 microns. The metal pigmentsare coated with an effective amount of a metal oxidecorrosion-inhibitor. The corrosion-inhibitor is derived from an aqueoussolution consisting essentially of trivalent chromium compounds,hexafluorozirconates, and at least one fluorocarbon selected from thegroup consisting of tetrafluoroborates, hexafluorosilicates, andhexafluorotitanates.

DETAILED DESCRIPTION

The invention relates to corrosion-inhibiting coated metal pigments andfilm-forming compositions thereof for coating metal substratesincluding, for example, substrates of aluminum, aluminum alloys, ironand various other ferrous metals such as steel.

The electrochemically corrosion-resistant metal-oxide coated pigmentsand the film-forming coating compositions of this invention forapplication to metal substrates consist essentially of coatedsacrificial-metal pigments having a particle size ranging from about 2to 100 microns coated with effective amounts of at least one metaloxide. The uncoated metal pigments are selected from the groupconsisting of zinc, magnesium, iron, aluminum, silver, copper andnickel. The coating consist essentially of metal oxides selected fromthe group consisting of chromium oxide, zirconium oxide and mixtures ofchromium and zirconium oxides in any ratios derived from an aqueouscomposition consisting essentially of, in parts by weight, from 0.01 to22 parts of a trivalent chromate, from 0.01 to 12 parts ofhexafluorozirconate, from 0.01 to 12 parts of a fluorocarbon selectedfrom the group consisting of tetrafluoroborate, hexafluorosilicate, andhexafluorotitanates, from about 0.0 to 12 or 0.01-12 parts of a divalentzinc compound and from 0.0 to 5.0 or 0.01 to 5.0 parts of a watersoluble corrosion inhibitor. The water soluble corrosion inhibitors areselected from the group consisting of benzimidazole, benzothiazole,benzoxazole, diphenyltriazole, benzotriazole, and tolytriazole.

More specifically, the electrochemically corrosion-resistantcompositions for application onto metal substrates consist essentiallyof, in parts by weight, from about

5 to 80 and preferably 20 to 80 parts of a film-forming binder selectedfrom the group consisting of an inorganic binder, polyurethanes,polyimides, polyacrylates, polymers derived from diisocyanates, polymersderived from epoxies and the uncured prepolymers of said polymers, fromabout 0.0 to 10 and preferably 0.1 to 10 parts of at least one organiccorrosion-inhibitor, from about 0.0 to 5.0 and preferably 0.1 to 1.5parts of at least one surfactant, from about 0.0 to 5.0 parts andpreferably 1.0 to 5.0 parts of solvent, and from about 20 to 80 andpreferably 50 to 70 parts of a coated sacrificial-metal pigment having aparticle size ranging from about 2 to 100 or 10 to 100 microns. Thesacrificial-metal pigments are coated with effective amounts of a metaloxide derived from a composition consisting essentially of, in parts byweight, an acidic aqueous solution comprising from about

0.01 to 22 parts of a trivalent chromium compound, from about

0.01 to 12 parts of hexafluorozirconate, from about

0.01 to 12 parts of at least one fluorocarbon selected from the groupconsisting of tetrafluoroborates, hexafluorosilicates, andhexafluorotitanates, from about 0.0 to 12 or 0.01-12 parts of at leastone divalent zinc compound, and from about

0.0 to 5 or 0.01-5 parts by weight of a water soluble corrosioninhibitor. The organic and water soluble corrosion inhibitors areselected from the group consisting of benzimidazoles, benzothiazoles,benzoxazoles, diphenyltriazoles, benzotrizoles, tolytriazoles andmixtures of said azoles in any ratio.

Another example of the electrochemically corrosion-resistantcompositions for application onto metal substrates consistingessentially of, in parts by weight, from about

5 to 80 parts of an oleaginous composition such as an organic lubricant,from about

0.0 to 10 or 0.1-10 parts of at least one organic corrosion inhibitor,from about

0.0 to 5.0 or 0.1-5 parts of at least one surfactant, from about

0.0 to 5.0 or 1.0-5 parts of organic solvent, and from about

20 to 80 parts of a sacrificial-metal pigment having a particle sizeranging from about 2 to 100 microns; said metal pigment coated witheffective amounts of at least one metal oxide such as chromium and/orzirconium oxides, derived from a composition consisting essentially ofan acidic aqueous solution having a ph of about 2.5-5.5 consistingessentially of from about

0.01 to 22 parts of a trivalent chromium compound, from about

0.01 to 12 parts of hexafluorozirconate, from about

0.01 to 12 parts of at least one fluorocarbon selected from the groupconsisting of tetrafluoroborates, hexafluorosilicates, andhexafluorotitanates, from about 0.0 to 5 and preferably 0.01-5 parts byweight of a water soluble corrosion inhibitor and from 0.0 to 12preferably 0.01-12 parts of a divalent zinc compound such as zincsulfate.

The organic corrosion inhibitors added to the coating composition areselected from the group consisting of benzimidazoles, benzothiazoles,benzoxazoles, diphenyltriazoles, benzotriazoles and tolyazoles.Effective amounts of solvent for the coatings, e.g., water or an organicsolvent ranges up to about 50%, e.g., from about 10-25% by weight of thewet coating.

The binder for the film-forming coating composition is selected from thegroup consisting of an inorganic binder such as the siloxanes, and theorganic polymers such as the polyacrylates, polyurethanes, polyimides,polymers derived from epoxies, polymers derived from isocyanates, andthe uncured pre-polymers or monomers of said polymers. The film-formingbinder also can be selected from the group consisting of inorganicpolymers derived from silanes, siloxanes and silicones.

Example 1 Composition and Process to Apply a Coating to 99.99% AluminumParticles or Powder Pigments

To one liter of distilled water, add 3.0 grams of basic chromiumsulfate, 4.0 grams of potassium hexafluorozirconate, and 0.12 gramspotassium tetrafluoroborate. Stir solution until all chemicals aredissolved in H₂O. Let stand for seven days before use to allow for theinorganic polymer of chromium sulfate to complex with the fluoride saltsand equilibrate. Dilute this solution to 40% by volume with distilledwater.

Add approximately 100 grams of spherical 20 micron 99.99% aluminum powerparticles to a one-liter flask. To the flask, add approximately 500milliliters of the inorganic polymers solution at ambient conditions andagitate or stir for approximately five minutes. The powder tends tosettle quickly in the solution so constant agitation is necessary. Afterfive minutes, decant off the inorganic polymer solution. The wet coatedpowder was added slowly to a large Buchner funnel with filter paper. Asthe wet slurry was added, a vacuum was applied. The powder was rinsedapproximately three times with distilled water to remove unreactednonorganic polymer solution. After rinsing, the powder cake and filterpaper were removed and placed on a large watch glass and allowed to dryat ambient conditions overnight. In the morning, the coated powder wasdry to handle and placed in a glass container and sealed.

Example 2 An Identical Process as Example 1, Except that the Metal beingCoated is 5 Micron of 99% Zinc Particles Example 3 Second Compositionand Process to Apply a Coating to Aluminum Particles

An identical process as Example 1, except that 2.0 grams per liter ofzinc sulfate was added to the inorganic polymer solution after reactingfor seven days and after diluting H₂O to 40 volume %.

Example 4 Third Composition and Process for Applying a Coating toAluminum Particles

An identical process as Example 1, except that the 20 micron 99.99% purealuminum particles were milled for 3 days in a horizontal ball mill tocreate flake-like particles before the coating process.

Example 5 Composition and Process to Apply a Coating to Iron Particles

An identical process as Example 1, except that the metal being coated is10 micron of 99.9% iron particles.

Example 6 Composition and Process to Apply a Coating to Nickel Particles

An identical process to Example 1, except that the metal being coated is10 micron of Ni particle agglomerate. The nickel was activated by anacid wash prior to being treated with the coating solution.

Example 7 Composition and Process to Apply a Coating to Silver Particles

An identical process as Example 1, except that the metal being coated is5 micron of 99% silver particles.

Example 8 Composition and Process to Apply a Coating to Phosphated IronParticles Example 9 Composition of a Conductive Grease Made with CoatedNickel Particles

Particles coated per Example 6 were blended with a liquidpolydimethylsiloxane to join the polymer coating up to the point wherethe composition had acceptable viscosity and properties to be spreadableonto a metal substrate. Approximately 11% of the coated powder wasblended into the polydimethylsiloxane.

Example 10 Composition of Corrosion-Resistant Primer Coating was Madewith Coated Zinc Particles of this Invention

Particles coated per Example 2 were used to make a corrosion-resistantprimer coating. Coated zinc was added to an epoxy resin with an aminecuring agent at approximately 58 volume percent. This coating was sprayapplied to aluminum alloy test panels of 2024-T3 and 7075-T6 and allowedto cure for 24 hours. After curing, the coatings were scribed to thebase metal and placed in ASTM B117 and ASTM G85 Annex 4 accelerated saltfog test cabinets. Panels were held in plastic racks at 15 degrees fromthe vertical. These coatings were compared to a similar epoxy coatingthat was prepared using uncoated zinc powder.

The inorganic and organic polymeric binders used for preparing thecorrosion-inhibiting pigment coating compositions range from about 5 to80 or 20 to 80 parts and preferably 30 to 50 or 50 to 70 parts by weightof the cured coatings. The film-form ing binders used in preparing thecoatings for substrates include polymers derived from the inorganicpolymers such as the siloxanes and the organic polymers including theepoxies, isocyanates, acrylics, and the uncured polymers or precursorsof these polymers including the polyimides and the precursors, i.e., thepolyamic acids. The imide polymers are well known and include polyimideprecursors derived from aromatic dianhydrides, polyamines and reactivecrosslinkable monofunctional endcaps. Preferred dianhydrides includepyromeliticdianhydride; benzophenone tetracarboxylic dianhydride;(hexafluoroisopropylidene)-bis(phthalic anhydride)biphenyltetracarboxylic dianhydride and benzophenone tetracarboxylicdianhydride. Various polyfunctional aromatic amines, including diamines,triamines and tetra-amines and mixtures thereof can be used to preparethe polyimide precursors or polymers.

Other known polymers include polymers of the epoxies or epoxy-resins orthe precursors, and polymers derived from isocyanates. For purposes ofthis invention, the term “epoxy precursors” includes epoxy or epoxiecompounds having one or more oxirane groups, i.e., an oxygen atom bondedto vicinal carbon atoms. Various precursors of epoxies particularlysuitable for purposes of this invention are precursors that are liquidat room temperature. Specifically, the epoxy precursors includecompounds which can be characterized either as saturated or unsaturatedaliphatic, cycloaliphatic, aromatic or heterocyclic compounds. Thecurable epoxy precursors may be prepared in various solvents includingorganic solvents which escape from the coating by evaporation during thecuring step. These solvents are well known and include, for example,esters such as butyl acetate, acetates of ethylene glycol monoethylether (Cellosolve acetate), methyl Cellosolve acetate, and the etheralcohols.

Another preferred binder for the corrosion-inhibiting metal coatingscomprises the polyurethanes derived from isocyanates and moreparticularly the aliphatic polyurethanes derived from the reaction ofpolyols and multifunctional aliphatic isocyananates. The polyol ispreferably used in an organic solvent e.g., toluene, xylene, n-butylacetate, methyllethyl ketone, etc. The hydroxyl number of the polyol,and the isocyanate (NCO) content or the equivalent weights of theisocyanate and polyol are determined in order to obtain the desiredpolyurethane. The preferred polyols and isocyanates are reacted inapproximately stoichiometric amounts so that the NCO to hydroxyl ratioranges from about 0.85 to 1.6 equivalent of the NCO to 1.0 equivalent ofthe OH. Specific compounds used in preparing these binders include, forexample, isocyanates such as: diphenylmethane-4.4′-diisocyanate,toluene2,4-diisocyanate, tetramethylene diisocyanate, decamethylenediisocyanate, ethylene diisocyanate, propylene-1,2-diisocyanate, and thelike. Preferred polyisocyanates include hexamethylene diiocyanate andmethylene-bis(4-cyclohexyl isocyanate) e.g., DISMODUR-N. By selectingthe proper polyols and by adjusting the NCO to OH ratio, the physicalproperties and efficiency of the film, such as the strength of film,flexibility, chemical resistance, solvent resistance, etc. can becontrolled over a wide range.

Examples of other binders include the polyacrylates, such as thepolyalkylacrylates, polymethacrylates, polymethylmethacrylate,polybutylmethacrylate, polyethylmethacrylate, polypropylmethacrylate,and combinations thereof. Also included as binders are the water solubleacrylics latex-emulsion coatings. Inorganic binders that can be used inthe present invention include those described in L. Smith ed., GenericCoating Types: An Introduction to Industrial Maintenance CoatingMaterials, Pittsburgh, Pa. This Technology Publication is incorporatedby reference. For example, the coating compositions prepared withinorganic binders which have a modified SiO₂ structure can be derivedfrom silicates, silanes, siloxanes or silicones. The coatings can beapplied to the substrate in the form of a suspension or solution in asuitable solvent such as water as in latex coatings or combination ofsolvents. Application can be carried, out for example, by any technique,such as spraying, brushing, rolling, flooding, immersion, to achieve asuitable coating thickness, ranging up to about ten (10) mils.

A variety of organic solvents are known which can be used for purposesof this invention in preparing organic coatings. The preferred solventsare substantially non-polar or oleophilic solvents. These solventsinclude aromatic or aliphatic hydrocarbons. Aromatic solvents includebenzene, toluene, xylenes, naptha, and fractions from the distillationof petroleum. Aliphatic hydrocarbon solvents include hexane,cyclohexane, heptanes, octanes and similar straight and branchedhydrocarbons and mixtures thereof, generally having 4-16 carbon atoms.Included are the aliphatic fractions from distillation of petroleumincluding mineral spirits and various mixtures of these solvents in anyratio. Aqueous systems include the acrylic resins well known for use inlatex coatings.

The wetting agents or surfactants used to apply the coatings to themetal surface or substrate are added to the coatings in amounts rangingfrom about 0.0-5.0 parts by weight and preferably in amounts rangingfrom about 0.1 to 2.0 or 0.1 to 1.5 part. These wetting agentspreferably include the lower weight glycols, such as ethylene orpropylene glycols, the aliphatic alcohols, alkoxyalcohols, ethers,etheralcohols, glycol ethers, and combinations thereof.

The viscosity or thickening of the coating may be adjusted for theparticular method of application by adding water for latex coatings orinert organic solvents for organic coatings. The coated metal surfacemay be dried by exposure to air or by baking. If the coating compositionis of correct viscosity, the coating or film can be applied directly tothe metal surface and baking may not be necessary. The film thicknessmay not be critical, however, an effective amount sufficient to form acoating ranges up to about 0.004 inches or more per square foot forcoatings.

In general, an effective amount of the corrosion-inhibiting resincoatings are applied onto the metal substrates or onto the metalpigments at thickness ranging from about 0.001 to 0.003 inches, e.g., upto ten mils or more. The coating may be applied onto the metalsubstrates by various methods including spraying, rolling, or brushingonto the metal substrate depending on the viscosity. The viscosity ofthe coating for the particular application may be achieved by adjustingthe content of the solvent within the ranges specified and by theselection of the particular reactants used to form the polymeric binder.

While this invention has been described by a number of specificexamples, it is obvious to one skilled in the art that there are othervariations and modifications which can be made without departing fromthe spirit and scope of the invention as particularly set forth in theappended claims.

The invention claimed is:
 1. A coated sacrificial-metal pigment having aparticle size ranging from about 2 to 100 microns said pigment is coatedwith an effective amount of at least one metal oxide selected from thegroup consisting of chromium oxide, zirconium oxide and mixtures ofchromium and zirconium oxides; the uncoated metal pigment selected fromthe group consisting of zinc, magnesium, iron, aluminum, silver, copperand nickel; said metal oxide coating derived from an acidic aqueouscomposition consisting essentially of, in parts by weight, from 0.01 to22 parts of a trivalent chromate, from 0.01 to 12 parts ofhexafluorozirconate, from 0.01 to 12 parts of a fluorocarbon selectedfrom the group consisting of tetrafluoroborate, hexafluorosilicate, andhexafluorotitanates, from about 0.01 to 12 parts of a divalent zinccompound and from 0.01 to 5.0 parts of a water-soluble corrosioninhibitor.
 2. The coated sacrificial-metal pigment of claim 1 whereinthe coated metal pigment is aluminum coated with mixtures of chromiumand zirconium oxides.
 3. The coated sacrificial-metal pigment of claim2, wherein the divalent zinc compound is zinc sulfate.
 4. The coatedsacrificial-metal pigment of claim 1, wherein the water solublecorrosion inhibitor is selected from the group consisting of abenzimidazole, a benzothiazole, a benzoxazole, a diphenyltriazole, abenzotriazole and a tolytriazole.
 5. The coated sacrificial-metalpigment of claim 1, wherein the uncoated metal pigment is aluminum. 6.The coated sacrificial metal pigment of claim 1, wherein the uncoatedmetal pigment is nickel.
 7. The coated sacrificial-metal pigment ofclaim 1, wherein the uncoated metal pigment is magnesium.
 8. The coatedsacrificial-metal pigment of claim 4, wherein the water solublecorrosion inhibitor is benzotriazole.
 9. The coated sacrificial-metalpigment of claim 1, wherein the aqueous composition has a pH of fromabout 2.5 to 5.5.
 10. An electrochemically corrosion-resistantcomposition for application onto metal substrates consisting essentiallyof, in parts by weight, from about 5 to 80 parts of a film-formingbinder selected from the group consisting of an inorganic binder,polyurethanes, polyimides, polyacrylates, polymers derived fromdiisocyanates, polymers derived from epoxies and the uncured prepolymersof said polymers, from about 0.0 to 10 parts of at least one organiccorrosion-inhibitor, from about 0.0 to 5.0 parts of at least onesurfactant, from about 0.0 to 5.0 parts of solvent, and from about 20 to80 parts of a coated sacrificial-metal pigment having a particle sizeranging from about 2 to 100 microns; said sacrificial-metal pigmentcoated with effective amounts of at least one metal oxide derived from acomposition consisting essentially of an acidic aqueous solutioncomprising from about 0.01 to 22 parts of a trivalent chromium compound,from about 0.01 to 12 parts of hexafluorozirconate, from about 0.01 to12 parts of at least one fluorocarbon selected from the group consistingof tetrafluoroborates, hexafluorosilicates, and hexafluorotitanates,from about 0.01 to 12 parts of at least one divalent zinc compound, andfrom about 0.0 to 5 parts by weight of a water-soluble corrosioninhibitor.
 11. The corrosion-resistant composition of claim 10, whereinat least one of the divalent zinc compounds is zinc sulfate.
 12. Thecorrosion-resistant composition of claim 10, wherein the pH of theacidic aqueous solution ranges from about 2.5 to 5.5.
 13. Thecorrosion-resistant composition of claim 10, wherein an effective amountof the oxide is coated onto the metal pigment in an amount ranging up toten mils of coating thickness.
 14. The corrosion-resistant compositionof claim 10, wherein the sacrificial metal pigment has a particle sizeranging from about 20-46 microns.
 15. The corrosion-resistantcomposition of claim 10, wherein the coated sacrificial metal pigmentranges from about 50 to 70 parts of the composition.
 16. Thecorrosion-resistant composition of claim 10, wherein the film-forminginorganic binder is polysiloxane.
 17. The corrosion-resistantcomposition of claim 10, wherein the solvent ranging from 1.0 to 5.0parts.
 18. An electrochemically corrosion-resistant composition forapplication onto metal substrates consisting essentially of, in parts byweight, from about 5 to 80 parts of an oleaginous composition consistingof an organic lubricant, from about 0.1 to 10 parts of at least oneorganic corrosion inhibitor, from about 0.1 to 5.0 parts of at least onesurfactant, from about 1.0 to 5.0 parts of organic solvent, and fromabout 20 to 80 parts by weight of a coated sacrificial-metal pigmenthaving a particle size ranging from about 2 to 100 microns; said metalpigment coated with an effective amount of at least one metal oxideselected from the group consisting of chromium oxide, zirconium oxideand mixtures of chromium and zirconium oxides derived from an acidicaqueous solution having a pH of about 2.5-5.5 consisting of from about0.01 to 22 parts of a trivalent chromium compound, from about 0.01 to 12parts of hexafluorozirconate, from about 0.01 to 12 parts of at leastone fluorocarbon selected from the group consisting oftetrafluoroborates, hexafluorosilicates, and hexafluorotitanates, fromabout 0.01 to 12 parts of at least one divalent zinc compound, and fromabout 0.01 to 5 parts by weight of a water soluble corrosion inhibitor.19. The corrosion-resistant composition of claim 18, wherein thedivalent zinc compounds is zinc sulfate.
 20. The corrosion-resistantcomposition of claim 18, wherein the lubricant is a grease composition.21. The corrosion-resistant composition of claim 18, wherein the metalpigment is coated with a mixture of chromium and zirconium oxides. 22.The composition of claim 18, wherein the metal pigment is coated withchromium oxide.
 23. The composition of claim 18, wherein the metalpigment is coated with zirconium oxide.
 24. The composition of claim 18wherein the water soluble corrosion inhibitor is an azole.
 25. Thecomposition of claim 24 wherein the azole is benzotriazole.
 26. Aprocess for preparing the coated sacrificial-metal pigment of claim 1which comprises coating said metal pigment with an effective amount ofat least one metal oxide selected from the group consisting of chromiumoxide, zirconium oxide and mixtures of chromium and zirconium oxides,said uncoated metal pigment selected from the group consisting of zinc,magnesium, iron, aluminum, silver, copper and nickel, said metal oxidecoating derived from an acidic aqueous composition consistingessentially of, in parts by weight, from 0.01 to 22 parts of a trivalentchromate, from 0.01 to 12 parts of hexafluorozirconate, from 0.01 to 12parts of a fluorocarbon selected from the group consisting oftetrafluoroborate, hexafluorosilicate, and hexafluorotitanates, fromabout 0.01 to 12 parts of a divalent zinc compound and from 0.01 to 5.0parts of a water soluble corrosion inhibitor.
 27. The process ofpreparing the coated sacrificial-metal pigment of claim 26 wherein thecoated metal pigment is aluminum coated with a mixture of chromium andzirconium oxides.